Component sheet and method of singulating

ABSTRACT

A sheet of electronic components includes a plurality of electronic components. A plurality of connecting members mechanically connects the electronic components together. A first fiducial marker is located at a first predetermined location on the sheet and a second fiducial marker is located at a second predetermined location on the sheet.

BACKGROUND

Shunt resistors are low resistance resistors that are used in manyelectronic devices and circuits to measure the current flow through acomponent or a circuit. The voltage drop across a shunt resistor ismeasured, which readily provides the current flow through the shuntresistor. The resistance of a shunt resistor is very low so as tominimize the effects of the shunt resistance on the circuit. If theshunt resistance is high, the shunt resistor will draw power from thecomponent or circuit from which it is measuring current. In addition tohaving low resistance, the shunt resistor has to pass all the currentflowing through the circuit or component. Accordingly, shunt resistorsare components that typically have high volumes so as to have lowresistance and the ability to conduct the current flow through thecomponent or circuit.

SUMMARY

A sheet of electronic components includes a plurality of electroniccomponents. A plurality of connecting members mechanically connects theelectronic components together. A first fiducial marker is located at afirst predetermined location on the sheet and a second fiducial markeris located at a second predetermined location on the sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a circuit that has a high current, lowresistance resistor that is functioning as a shunt resistor.

FIG. 2 is a side isometric view of the interior of an exemplaryintegrated circuit package that includes an integrated circuit die and ashunt resistor.

FIG. 3A is a top plan view of a sheet having a plurality of resistorsformed therein.

FIG. 3B is an enlarged view of a single resistor on the sheet of FIG.3A.

FIG. 4 is a top plan view of the sheet of FIG. 3A in a misalignedposition relative to a singulating device.

FIG. 5 is a top plan view of the sheet of FIG. 4 being analyzed todetermine its orientation.

FIG. 6 is a top plan view of a sheet of resistors having fiducialmarkers located on specific resistors.

FIG. 7A is an example of a fiducial in the shape of a cross.

FIG. 7B is an example of a T-shaped fiducial.

FIG. 8 is a flow chart describing a method of aligning a sheet ofcomponents to a singulating device.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of a circuit 100 that has high current, lowresistance resistor R10 that is functioning as a shunt resistor. Thecircuit 100 is an example of one of numerous circuit designs that use alow resistance, high current resistor as a shunt resistor. The circuit100 includes a power supply 110 that supplies power to components andcircuitry within the circuit 100. Power circuitry 112 generates anoutput signal that conducts through the shunt resistor R10. The currentpassing though the shunt resistor oRIO generates a sensing voltageV_(SENsE) that is proportional to the current. A controller 114 monitorsthe sensing voltage V_(SENSE) and controls the power circuitry inresponse to the sensing voltage V_(SENSE).

The resistance of the shunt resistor R10 is very low in order tominimize the effects of the shunt resistor R10 on the other componentsin the circuit 100. If the resistance of the shunt resistor R10 washigh, the shunt resistor R10 would expend power that would otherwise beconducted to the output. In addition to having low resistance, the shuntresistor R10 has to pass all the current flowing from the powercircuitry 112 to the output. Accordingly, shunt resistors, such as theshunt resistor R10, are components having high volume and/or a largecross section so as to have low resistance and the ability to conducthigh current. The high volume of shunt resistors makes them impracticalto be fabricated into or physically attached to most integrated circuitdies. Some resistors used as shunt resistors are fabricated from copperalloy.

FIG. 2 is a side isometric view of the interior of an exemplaryintegrated circuit package 200 that includes an integrated circuit die204 and a resistor R20. The package 200 may include other devices thatsecure the die 200 in its locations shown in FIG. 2. In the example ofFIG. 2, the resistor R20 has low resistance and the capability ofpassing high current, such as the current conducted through a shuntresistor. Both the die 204 and the resistor R20 are mechanically andelectrically coupled to a lead frame 208 having leads 210 extending froma first side 212 and leads 216 extending from a second side 218. The die204 is electrically coupled to the leads 210 and 216 by way of wirebonds 220. The die 204 draws relatively little current, so conventionalwire bonds 220 are sufficient for coupling the die 204 to the leads 210on the first side 212 and the leads 216 on the second side 218 of thelead frame 208.

The resistor R20 functions as a shunt resistor, so the die 204 likelydoes not have the current handling capability of the resistor R20. Theresistor R20 may be fabricated from the materials described above so asto be a block of conductive material, such as a block of copper alloy.The resistor R20 has a first end 230 and a second end 232. The ends 230and 232 are coated with a conductive adhesive to mechanically andelectrically couple the resistor R20 to the leads 210 on the first side212 of the lead frame 208 and the leads 216 on the second side 218 ofthe lead frame 208. In order to handle the current flow requirements ofthe resistor R20 when it is used as a shunt resistor, the first end 230is electrically coupled to a plurality of leads 240 and the second end232 is electrically coupled to a plurality of leads 242. The resistorR20 has pads or other locations for receiving wire bonds 244 and 246,which are coupled to leads 248 and 250, respectively. The leads 248 and250 are for measuring a sensing voltage V_(SENSE) generated by currentflow through the resistor R20 as described with reference to FIG. 1.

The resistor R20 is singulated from a sheet of resistors as a small chipmodule separate from the die 204 and prior to placement within thepackage 200. Prior to singulation of the resistors, auto saw alignmentis required to be performed in order to correctly cut the resistors tothe correct size and shape. A singulating device, such as a saw or thelike, singulates the resistors from the sheet of resistors. Conventionalauto saw alignment methods used in silicon wafer dicing depend on devicechip (die) unique features for alignment reference and are not suitablefor singulating resistors such as the resistor R20.

FIG. 3A is a top plan view of a sheet 300 having a plurality ofresistors 302 formed therein and FIG. 3B is an enlarged view of a singleresistor 304. In some examples, the whole sheet 300 is fabricated fromthe material of the resistors 302, such as the copper alloy describedabove. The sheet 300 may be stamped or processed, such as etched, toform the individual resistors 302 shown in FIG. 3A and the resistor 304shown in FIG. 3B. As shown in FIG. 3B, a plurality of connection members306 connect individual resistors to each other to form the sheet 300 ofresistors. The connection members 306 are located between cut-outportions 307 of the sheet. These connection members 306 have to be cutto singulate the individual resistors from one another. If the cuttingis not aligned with the connection members 306, the singulating orcutting device may contact resistors, which will damage or destroy theresistors.

In the example of FIG. 3A, the resistors 302 are arranged in an arrayhaving a plurality of rows 308 and columns 310, which are orthogonal.The sheet has a first edge 312, a second edge 314, a third edge 316, anda fourth edge 318. The sheet 300 includes a plurality of fiducialmarkers, which are referred to herein as “fiducials,” to provide pointsof reference for singulating operations. The fiducials may be virtuallyany marker having a shape that is able to be imaged by an imaging deviceas described below. The fiducials are located at predetermined locationson the sheet 300. Therefore, when the fiducials are imaged, an imagingsystem can correlate the locations of the images of the fiducial with asingulation device to perform accurate singulation as described below.

In the example of FIG. 3A, the fiducials 320 on the sheet 300 areT-shaped fiducials. Further to the example of FIG. 3A, the fiducials areoriented in four directions depending on their locations on the sheet300. In other examples, the fiducials 320 are not oriented in anyspecific direction, but are placed at predetermined locations on thesheet 300. A fiducial 322 provides an example of a first orientationwherein the T-shaped fiducial is referred to here as being upright. Inthe example of FIG. 3, fiducials having the first orientation arelocated proximate the first edge 312 of the sheet 300. A fiducial 324provides an example of a second orientation wherein the T-shapedfiducial is rotated clockwise ninety degrees from the first orientation.The orientation of the fiducial 324 is referred to herein as beingrotated right. In the example of FIG. 3A, fiducials having the secondorientation are located proximate the second edge 314. A fiducial 326provides an example of a third orientation wherein the T-shaped fiducialis oriented upside down with reference to the first orientation. Thethird orientation is referred to herein as the inverse orientation. Inthe example of FIG. 3A, fiducials having the third orientation arelocated proximate the third edge 316. A fiducial 328 provides an exampleof a fourth orientation, wherein the T-shaped fiducial 328 is rotatedninety degrees counter clockwise relative to the first orientation. Thefourth orientation is referred to herein as being rotated left. In theexample of FIG. 3A, fiducials having the fourth orientation are locatedon the fourth edge 318.

In other examples, the different orientations of the fiducials mayindicate a corner of the sheet 300. More specifically, fiducials havingthe first orientation may be located proximate a first corner, fiducialshaving a second orientation may be located proximate a second corner andso on. In some examples, the horizontal portion of an upright “T” islocated a predetermined distance from the edge of the sheet and thevertical portion of the “T” is located at a predetermined location onthe sheet 300.

The fiducials 320 provide orientation markers for visual alignment ofthe sheet 300 relative to a singulating device or the like (not shown inFIG. 3A) that singulates the resistors 302. The horizontal bar infiducials having the first orientation, such as the fiducial 322,provide an indication as to the location of the first side 312. Thevertical portions of the fiducials 320 provide a first indication as tothe orientation of the sheet 300. Accordingly, fiducials having thefirst orientation are correlated with the first edge 312 of the sheet300 by an imaging system. The same applies to the third orientation,such as with the fiducial 326 wherein the vertical portion extending uppoints toward the interior of the sheet 300, so the imaging systemcorrelates the third orientation with the third edge 316. The verticalportions of the fiducials on the second and third edges 314 and 318provide indications that the fiducials are located proximate the edges314 and 318. The horizontal portions of the fiducials indicate the edgeof the sheet 300 on which the fiducials are located. When the horizontalportion is to the left of the vertical portion, the fiducial is locatedproximate the second edge 314 and when the horizontal portion is to theright of the vertical portion, the fiducial is located proximate thefourth edge 318.

In addition to providing indications as to the locations of the edges ofthe sheet 300, the fiducials 320 also provide information regarding thelocation of the sheet 300. The fiducials 320 are located atpredetermined locations on the sheet 300. For example, the fiducials 320may be located at predetermined distances from the edges. When animaging system locates and identifies a fiducial, it can readilydetermine the location of the sheet 300 based on the location of thefiducial. As described in greater detail below, the location informationis used to determine the alignment and/or orientation of the sheet 300relative to a singulating device prior to cutting or singulating theindividual resistors 302 from the sheet 300.

FIG. 4 shows the sheet 300 in a misaligned position relative to asingulating device 450. In the example of FIG. 4, the singulating device450 operates along the X-Y coordinates of the Cartesian plane shown inFIG. 4. The sheet 300 and/or the singulating device 450 must be rotatedso that they are aligned prior to singulating the resistors 302,otherwise the resistors 302 will be damaged during the singulatingprocess. An imaging system 400 captures images of the sheet 300 andidentifies the fiducials and their locations, which is indicative of thelocation and orientation of the sheet 300. For example, the imagingsystem 400 may include a processing component that identifies thefiducials and their orientations. The sheet and/or the singulatingdevice 450 are then oriented to singulate the resistors 302 withoutdamaging the resistors 302. For example, an aligning component (notshown) may orient or align the sheet and/or the singulating device 450.

In the example of FIG. 4, the imaging system 400 captures an imageproximate the intersection of the third edge 316 and the fourth edge 318of the sheet 300 where a fiducial 404 and a fiducial 406 are located. Inthis example, the imaging system 400, or a processing componentassociated with the imaging system 400, identifies the fiducial 404,which is shown with an enlarged view. The fiducial 404 has the fourthorientation, so it has a vertical portion 412 with a horizontal portion414 extending to the right. The vertical portion 412 and the horizontalportion 414 intersect at an intersection 416. The imaging system 400identifies the right extending vertical portion 414 as a fiduciallocated proximate the fourth edge 318. In some examples, the imagingsystem 400 may analyze characteristics of the fiducial 406 to determinethat it is imaging an area of the sheet 300 proximate the third edge 316and the fourth edge 318.

The imaging system 400 images a second fiducial to obtain information toascertain the orientation of the sheet 300 relative to the singulatingdevice 450. In the example of FIG. 4, the imaging system 400 images asecond fiducial 420 that is located proximate the second edge 314 of thesheet 300 and has the second orientation. The fiducial 420 has avertical portion 422 with a horizontal portion 424 extending from theleft of the vertical portion 422. The horizontal portion 424 and thevertical portion 422 intersect at an intersection 426. The imagingsystem 400 identifies the horizontal portion 424 extending to the leftof the vertical portion 422 as being a fiducial located proximate thesecond edge 314. The location of the intersection 426 provides thelocation and orientation of the sheet 300 relative to the singulatingdevice 450.

FIG. 5 is a top plan view of the sheet 300 of FIG. 4 being analyzed todetermine its orientation. The imaging system 400 or a componentassociated therewith has determined the locations of the fiducials 404and 420, which are located at predetermined positions on the sheet 300.The imaging system 400 generates an axis 500 that intersects bothintersections 416 and 426 of the fiducials 404 and 420, respectively.The axis 500 is compared to an axis 502 that is parallel to the x-axisof the Cartesian plane, which is associated with the sawing directionsof the singulating device. The imaging system 400 generates signals torotate the sheet 300 and/or the singulating device so that the axes 500and 502 are parallel. When the axes 500 and 502 are parallel, thesingulating device 450 may cut the sheet 300 to form individualresistors 302.

The sheet 300 has been described above as having T-shaped fiducials 320located at predetermined locations on the sheet 300. The fiducials mayhave other shapes that enable an imaging system to locate them. Forexample, the fiducials may be X-shaped or the fiducials may be round.The fiducials may be placed on the sheet 300 by a plurality of differentmethods. For example, the fiducials may be printed, stamped, plated, oretched onto or into the sheet 300. The sheet 300 has been describedherein as being a sheet of resistors. In other examples, the sheet mayinclude other components, such as other discrete components or othermetal components.

In some examples, the fiducials are placed on the resistors in thesheet. FIG. 6 is a top plan view of a sheet 600 of resistors havingfiducials located on resistors. In the example of FIG. 6, four resistorslocated in the corners of the sheet 600 have fiducials located thereon.The resistors having fiducials located thereon are a first resistor 610located in an upper left corner, a second resistor 612 located in anupper right corner, a third resistor 614 located in a lower rightcorner, and a fourth resistor 616 located in a lower left corner. Thefiducials on these resistors 610-616 are used to identify the locationand orientation of the sheet 600 in the same manner as described aboveexcept that the fiducials are located on resistors instead of the edgesof the sheet 300, FIG. 3A.

FIGS. 7A and 7B are examples of different fiducials that may be appliedto the resistors or the sheets. FIG. 7A is an example of a fiducial 700in the shape of a cross. The cross has a horizontal portion 710 and avertical portion 712 that intersect at an intersection 714. Thecombination of the horizontal portion 710, the vertical portion 712, andthe intersection 714 provide imaging information to enable the imagingsystem 400, FIG. 4, to determine the location and orientation of thesheet 600, FIG. 6. In the example of FIG. 7A, the fiducial 700 includesspots 718 that distinguish the fiducial 700 from other artifacts thatmay be imaged by the imaging system 400. In some embodiments, thefiducial 700 is rotated forty-five degrees to form an X-shaped fiducial.

FIG. 713 is an example of a T-shaped fiducial 730. The fiducial 730 mayhave the same orientation on all the resistors 610-616, FIG. 6. In otherexamples, the fiducial 730 has a different orientation depending onwhich corner it is located. The imaging system 400, FIG. 4, may thenreadily determine the location and orientation of the sheet 600, FIG. 6.

Having described various fiducials and different locations of thefiducials on a sheet of components, the singulating device and methodsof singulating will now be described. Reference is made to FIG. 4 wherethe sheet 300 is misaligned with a singulating device 450, and whereinthe singulating device 450 operates or cuts along the Cartesian plane ofFIG. 4. The imaging system 400 images the fiducial 404 and determinesthe location of the fiducial 404, such as. the location of theintersection 416. Simultaneously or subsequently, the imaging system 400images the fiducial 420, such as the intersection 426. By analyzing thelocations of the fiducials 404 and 420, the imaging system 400 is ableto determine the location and orientation of the sheet 300. One exampleof this analysis is shown by the axes 500 and 502 of FIG. 5 whereinnon-parallel axes is an indication of the sheet 300 and the singulatingdevice 450 not being oriented together. In response to the analysis, thesheet 300 and/or the singulating device 450 is reoriented and first cutsto singulate the resistors 302 may be performed. The orientation enablesthe singulating device 450 to cut the connecting members 306, FIG. 3B,without damaging resistors 302 or other components.

The sheet 300 may be rotated ninety degrees to perform second cuts thatare orthogonal to the first cuts. The imaging system 400 may performanother analysis to determine if the rotated sheet is oriented with thesingulating device 450 as described above. Accordingly, the sheet 300and/or the singulating device 450 may be rotated so that they areproperly oriented to perform the orthogonal cuts.

FIG. 8 is a flow chart 800 describing a method of aligning a sheet ofcomponents to a singulating device. In step 802 a first fiducial markerlocated at a predetermined location on the sheet of components isimaged. In step 804 a second fiducial marker located at a predeterminedlocation on the sheet of components is imaged. The method continues withdetermining the orientation of the sheet of components in response toimaging the first fiducial marker and imaging the second fiducial markerat step 806. At step 808 the method includes aligning the sheet ofcomponents and the singulating device in response to determining theorientation of the sheet of components.

While some examples of component sheets and orientation methods havebeen described in detail herein, it is to be understood that theinventive concepts may be otherwise variously embodied and employed andthat the appended claims are intended to be construed to include suchvariations except insofar as limited by the prior art.

What is claimed is:
 1. A sheet of electronic components, the sheetcomprising: a plurality of electronic components; a plurality ofconnecting members that mechanically connect the electronic componentstogether; a first fiducial marker located at a first predeterminedlocation on the sheet; and a second fiducial marker located at a secondpredetermined location on the sheet.
 2. The sheet of claim 1, whereinthe electronic components are resistors.
 3. The sheet of claim 1,wherein the electronic components are aligned in an array of parallelcolumns and parallel rows.
 4. The sheet of claim 1, wherein the firstfiducial marker has a first orientation and the second fiducial markerhas a second orientation.
 5. The sheet of claim 1, wherein the sheetincludes: a first side with a first fiducial marker located proximatethe first side; a second side with a second fiducial marker locatedproximate the second side; a third side with a third fiducial markerlocated proximate the third side; and a fourth side with a fourthfiducial marker located proximate the fourth side.
 6. The sheet of claim5, wherein: the first, second, third, and fourth fiducial markers havethe same shape; the first fiducial marker has a first orientation; thesecond fiducial marker has a second orientation; the third fiducialmarker has a third orientation; and the fourth fiducial marker has afourth orientation.
 7. The sheet of claim I, wherein the sheet includes:a first corner with a first fiducial marker located proximate the firstcorner; a second corner with a second fiducial marker located proximatethe second corner; a third corner with a third fiducial marker locatedproximate the third corner; and a fourth corner with a fourth fiducialmarker located proximate the fourth corner.
 8. The sheet of claim 7,wherein: the first, second, third, and fourth fiducial markers have thesame shape; the first fiducial marker has a first orientation; thesecond fiducial marker has a second orientation; the third fiducialmarker has a third orientation; and the fourth fiducial marker has afourth orientation.
 9. The sheet of claim 1, wherein at least one of thefirst fiducial marker and the second fiducial marker are etched into thesheet.
 10. The sheet of claim 1, wherein at least one of the firstfiducial marker and the second fiducial marker are plated onto thesheet.
 11. The sheet of claim 1, wherein at least one of the firstfiducial marker and the second fiducial marker are located on at leastone of the components.
 12. A device for singulating components from asheet of components, the device comprising: a singulating device forsingulating individual components from the sheet of components; animaging system for imaging a plurality of fiducial markers located atpredetermined locations on the sheet; a processing component fordetermining the alignment of the sheet in response to imaging theplurality of fiducial markers; and an aligning component for moving atleast one of the singulating device and the sheet of components toachieve a predetermined orientation in response to determining thealignment of the sheet.
 13. The device of claim 12, wherein the sheet ofcomponents has a plurality of corners and wherein at least one of thefiducial markers is located proximate at least one of the plurality ofcorners.
 14. The device of claim 12, wherein the sheet of components hasa plurality of sides and wherein at least one of the fiducial markers islocated proximate at least one of the plurality of sides.
 15. The deviceof claim 12, wherein the imaging system includes a component fordetermining the orientation of fiducial markers.
 16. A method ofaligning a sheet of components with a singulating device, the methodcomprising: imaging a first fiducial marker located at a predeterminedlocation on the sheet of components; imaging a second fiducial markerlocated at a predetermined location on the sheet of components;determining the orientation of the sheet of components in response toimaging the first fiducial marker and imaging the second fiducialmarker; and aligning at least one of the sheet of components and thesingulating device in response to determining the orientation of thesheet of components.
 17. The method of claim 16, further comprisingdetermining the orientation of at least one of the first fiducial markerand the second fiducial marker.
 18. The method of claim 16, wherein thesheet of components has a plurality of edges and at least one of thefirst fiducial marker and the second fiducial marker is locatedproximate at least one of the plurality of edges.
 19. The method ofclaim 16, wherein at least one of the first fiducial marker and thesecond fiducial marker is located on a predetermined one of thecomponents.
 20. The method of claim 19, wherein determining theorientation of at least one of the sheet of components includes fittingan axis between an image of the first fiducial marker and the secondfiducial marker and comparing the axis to an axis associated with thesingulating device.